A non-scanning sonar indicating in three dimensions

Most sonar systems determine the bearing of an incoming signal either by scanning a beam through space or by examining the outputs of several preformed beams. Signal bearing may also be determined by operating on the set of relative signal amplitudes derived from four or more hydrophone arrays. So long as the set of relative responses is uniquely related to signal bearing, direction may be determined unambiguously. A simple form of array group leading to a unique solution in three dimensions is a set of three mutually perpendicular acoustic dipoles plus an omnidirectional sensor. By correlating each of the dipole outputs with the omnidirectional output and normalizing, the direction cosines of the received signal bearing are obtained. In the active sonar case, the region under observation may be illuminated by a pulsed source. The direction cosines may then be multiplied by range and applied to a pair of cathode ray tubes to show the plan view and side elevation for the region. Since system performance will be degraded by the occurrence of multiple echoes within one range resolution cell, the system is susceptible to adverse reverberation conditions. The receiver will function over a very wide bandwidth (greater than a decade), however, and thus range resolution may be made very great. The system may also be made ´foolproof´ under conditions permitting all significant targets to carry transponders. As such, the system may be quite useful in observing or supervising underwater diving operations.